1. Field of the Invention
The present invention relates to a display device and a mobile device using the display device, and more particularly, to a mobile device including display panels and a timing controller supplying signals to the display panels.
2. Discussion of the Related Art
Flat panel display (FPD) devices having portability and low power consumption have been the subjects of recent research and development since the coming of the information era. Specifically, a liquid crystal display (LCD) device, a plasma display panel (PDP) device, an electroluminescent display (ELD) device and a vacuum fluorescent display (VFD) device have been developed as FPD devices. Among the various types of FPD devices, liquid crystal display (LCD) devices are widely used as monitors for notebook computers and desktop computers instead of cathode ray tube (CRT) because of their high resolution, color quality and superior image movement.
In general, an LCD device includes a first substrate, a second substrate and a liquid crystal layer between the first and second substrates. Electrodes are formed on inner surfaces of the first and second substrates, and an electric field is generated between the electrodes when a voltage is applied. The LCD device uses the optical anisotropy and polarization properties of liquid crystal molecules to produce an image. Due to the optical anisotropy of the liquid crystal molecules, refraction of light incident onto the liquid crystal molecules depends upon the alignment direction of the liquid crystal molecules. The liquid crystal molecules have long thin shapes that can be aligned along specific directions. The alignment direction of the liquid crystal molecules can be controlled by applying the electric field generated between electrodes on the first and second substrates. Accordingly, the alignment of the liquid crystal molecules changes in accordance with the direction of the applied electric field. Thus, by properly controlling the electric field applied to a group of liquid crystal molecules within respective pixel regions, a desired image can be produced by appropriately modulating transmittance of the incident light.
There are several types of LCD devices, one of which is commonly referred to as active matrix LCD (AM-LCD) device. The AM-LCD device includes an array of pixels forming a matrix. Each of the pixels in the AM-LCD device includes a thin film transistor (TFT) and a pixel electrode. The AM-LCD devices are currently being developed because of their high resolution and superior quality for displaying moving pictures.
An LCD device displays images using the RGB data and several control signals transmitted from an external driving system. A low voltage differential signaling (LVDS) interface is used for a high-speed data transmission between the LCD device and the external driving system.
FIG. 1 is a schematic block diagram showing a liquid crystal display device and an external driving system according to the related art. In FIG. 1, an external driving system includes a graphic card 10 having a low voltage differential signaling (LVDS) transmitting portion 12 and an interface board 14 having an LVDS receiving portion 16, and a liquid crystal display device includes a timing controller 20, a gate driver 22 and a data driver 26 and a liquid crystal display panel 30. For example, the external driving system may include a computer body. The graphic card 10 transmits the RGB data and control signals of a transistor transistor logic (TTL) type to the LVDS transmitting portion 12. The control signals may include a data enable signal, a horizontal sync signal, a vertical sync signal and a system clock. The RGB data and the control signals are converted into communication signals of an LVDS type in the LVDS transmitting portion 12. The communication signals are transmitted to the LVDS receiving portion 16 of the interface board 14. The communication signals are re-converted into the RGB data and the control signals of a TTL type in the receiving portion 16. The RGB data and the control signals of a TTL type are transmitted to the timing controller 20. The timing controller 20 determines a timing format for the RGB data and the control signals of a TTL type, and generates a data signal and a gate signal. The data signal and the gate signal are transmitted to the data driver 26 and the gate driver 22, respectively.
The liquid crystal display panel 30 includes first and second substrates facing and spaced apart from each other. A plurality of gate lines 24 and a plurality of data lines 28, which are connected to the gate driver 22 and the data driver 26, respectively, are formed on the first substrate. The gate line 24 crosses the data line 28 to define a pixel region “P,” and a thin film transistor (TFT) “T” is connected to the gate line 24 and the data line 28. A pixel electrode connected to the TFT “T” is formed in the pixel region “P.” A black matrix (not shown) having an open portion, a color filter layer in the open portion and a common electrode on the color filter layer are formed on the second substrate. A liquid crystal layer between the pixel electrode and the common electrode constitutes a liquid crystal capacitor “Clc” with the pixel electrode and the common electrode. As a result, the gate signal of the timing controller 20 is transmitted to the plurality of gate lines 24 through the gate driver 22 and the data signal of the timing controller 20 is transmitted to the plurality of data lines 28 through the data driver 26.
When the TFT is turned on by the gate signal applied to the selected gate line 24, the liquid crystal capacitor “Clc” is charged by the data signal applied to the corresponding data line 28. Accordingly, the alignment direction of the liquid crystal molecules is changed in accordance with the data signal, thereby changing transmittance of the pixel region. Since the liquid crystal is not a self-emissive material, a backlight unit supplying light is disposed under the liquid crystal display panel 30 as a light source. As a result, the liquid crystal display panel 30 displays various images due to variance of transmittance and combination of colors through the color filter layer.
Recently, a multi-monitor where at least two LCD devices are connected to a single graphic card has been suggested due to the significant increase of information to be displayed. In the multi-monitor, different images are respectively displayed in the at least two LCD devices. A dual monitor having two LCD devices will be illustrated hereinafter as an example.
FIG. 2 is a schematic block diagram showing a dual monitor according to the related art. In FIG. 2, a dual monitor includes an external driving system and two liquid crystal display devices. The external driving system includes a graphic card 10 having first and second low voltage differential signaling (LVDS) transmitting portions 12a and 12b, a first interface board 14a having a first LVDS receiving portion 16a, and a second interface board 14b having a second LVDS receiving portion 16b. The first liquid crystal display device connected to the first interface board 14a includes a first timing controller 20a, a first gate driver 22a and a first data driver 26a and a first liquid crystal display panel 30a. The second liquid crystal display device connected to the second interface board 14b includes a second timing controller 20b, a second gate driver 22b and a second data driver 26b and a second liquid crystal display panel 30b. 
As shown in the dual monitor according to the related art, two interface boards 16a and 16b and two LCD devices are independently connected to the single graphic card 10. Accordingly, a dual monitor has several limitations. First, since two interface boards and two LCD devices having the same structure are used, a large size is required. Even though the substantial object of a dual monitor is to display more information in a smaller area, it is not effective due to the size increase, and a structure becomes complicated due to the individual interface boards and LCD devices. Second, two LCD devices do not perfectly display a single image as a whole. In a dual monitor according to the related art, individual RGB data and control signals are transmitted to the first and second timing controllers 20a and 20b from independent first and second LVDS transmitting portions 12a and 12b of the graphic card 10. Accordingly, the two LCD devices display may different images unless the graphic card includes a specific application for synchronization. A tiled LCD device where a plurality of liquid crystal display panels display a single image has been suggested. However, individual sub-images for the single image are displayed using individual RGB data and control signals in the tiled LCD device. As a result, the tiled LCD device has some disadvantages such as delays between frames and abnormality in picture change. In addition, duplicate high cost circuit elements such as timing controllers are required, and display quality is deteriorated due to separation of image.